A basic understanding of the cell in health and disease is essential if we are to understand more complex tissue, organ and organisms function. The major goals listed in the previous application for funds were 1) define kinetic and thermodynamic criteria useful in identification of alkali metal/H exchange, 2) investigate underlying control of alkali metal/H exchange, and 3) apply the model to analysis of cell volume disturbances (cardiac) in isotonic media. Our goal with regard to the first point has been largely realized. With respect to point 2, we have identified a number of activators of alkali metal/H exchange, completed studies of pH regulation ,and gained an understanding of anion effects. The control of Na/H exchange is sufficiently complex that we have begun biochemical studies in order to appropriately address the problem. In regard to point 3, we have applied NMR to Na transport by red cells and heart. The first phase of the studies evaluating the role of Na/H exchange in hypoxic cell damage is progressing nicely. In summary, aims for the period for which funds are requested are logical extensions of those previously stated. We propose to build upon our previous achievements, extending the applications and ideas developed through our past efforts. Thus, the proposal for funds is focused on increasing understanding of a fundamental cellular process, the Na/H exchanger. The Na/H exchange is broadly distributed and plays a central role in a variety of cellular processes which include (1) cell volume regulation, (2) cell pH regulation, (3) normal and abnormal cell growth, and (4) fluid-electrolyte and acid- base balance at the level of the organism. In light of the above, we propose to identify the Na/H exchange protein and ultimately evaluate its role as a kinase substrate in response to a variety of stimuli known to activate the exchanger. These studies will be performed employing conventional chemical and biochemical methods, using the Amphiuma red blood cell as a model. A second phase of the proposed studies is to evaluate the contribution of Na/H exchange to hypoxic/ischemic injury in the Langendorff perfused rabbit heart using NMR spectroscopy. We hypothesize that during hypoxia and ischemia the Na/H exchanger, operating in a pH regulatory role, causes Na uptake, cell swelling, Ca entry and ultimately cell death. By employing 23Na, 31P and 19F (BAPTA) spectroscopy and thermodynamic and pharmacologic criteria, we will evaluate Na/H exchange flux and its interplay with Na/Ca exchange, the Na-K pump and ultimately cell metabolism during hypoxia. The information to be obtained in the second phase is clinically significant as it relates to organ preservation and shipment for transplant, open heart surgery, shock, stroke, trauma and the like.